To ascertain whether employees who have been exposed to "permissible" levels of external and/or internal radiation have been harmed. Criterion of health used is the disability claim rate. The study population: 33,500 Hanford employees, 19,000 siblings of these employees, and 32,000 matched controls. Preliminary findings on the basis of 5,658 disability claims are: for males (24,345 employees; 4,770 claims) age-cohort adjusted claim rates lowest for employees when compared with the controls. When employees are divided into those with a record of exposures to occupational radiation, and those without, the exposed employees have the lowest claim rates vis-a-vis the other three groups; conversely the nonexposed have the highest claim rate when compared with the other three groups. For females the claim rate is highest for the employee; this is also true both for exposed and nonexposed employees compared with siblings and matched controls. However, the claim rates for exposed and nonexposed employees are about the same. These findings are consistent with comparative longevity of these same population groups. The study will continue with enlarged number of disability claims, in-depth information on such claims, and the addition of early retirement and completeness of retirement as additional measures of health.